1. Field of the Invention
The present application relates to an optical module, in particular, the present application relates to an optical module having an optical unit that encloses a semiconductor optical device with a sensitive surface whose level is aligned with an end surface of a housing to which the optical unit is fixed.
2. Background Arts
A wavelength division multiplexing (WDM) and/or a bi-directional communication using two wavelengths for a single optical fiber have been become popular by utilizing the orthogonality with respect to the wavelength. Also, the communication speed, or the communication capacity of such a system reaches and sometimes exceeds 10 Gbps. A light-receiving device, typically, a semiconductor photodiode (PD) and an avalanche photodiode (APD), is strongly requested to decrease parasitic capacitance including junction capacitance thereof. Accordingly, an optically sensitive area of such a PD has become narrower, where a diameter of the optically sensitive area is, for example, 30 μm or shorter to reduce the junction capacitance. The assembly of the optical module implementing such PD with a narrowed sensitive area has become critical because of a limited positional tolerance in the optical alignment thereof.